1. Field of the Invention
This invention relates generally to the field of radiography with mammography and differential angiography being particular examples. More particularly, this invention relates to a new and improved method and apparatus for conducting internal biological imaging.
2. Prior Art
One of the ubiquitous health hazards in todays world is mammarian malignancy. The disease, otherwise known as breast cancer, affects a significant number of women worldwide each year. Because of the staggering number of affected women and the deadly potential of the disease, much research has been carried out to better the chances of detection of the disease at an early stage, where the likelihood of successful treatment is substantially more promising.
Radiography for the discovery of anomalous features such as tumors in mammography, rely on the anomalous features having different x-ray absorption properties when compared to normal features. In general, the contrast produced in x-ray images between anomalous material and normal material varies with the wavelength of the x-rays used. Improved detection of anomalies can be achieved by using selective wavelengths. For example, in state of the art mammography, filters are used to block a fraction of the most radiation above about 17 thousand electron volts (17 Kev). As is axiomatic, however, all of the radiation below 17 Kev is allowed to pass into the specimen being evaluated as are some of the higher energy components. The excess radiation above and below 17 Kev is an unnecessary hazard to the specimen exposed, and from an even more practical point of view, the excess radiation degrades the image produced thereby. Therefore, alternate methods and apparati for mammographies have been sought.
Recent studies have shown that by using the very bright monochromatic radiation available from a few national selected facilities, improved detection can be achieved. However, the present availability of monochromatic radiation producing apparati, and concomitant cost thereof is far too limiting for general medical use.
Very bright monochromatic radiation is available from a few selected synchrotron facilities. This costly apparatus with its limited availability is discussed in detail in the volume 5, number 5, 1992 edition of Synchrotron Radiation News. It is obvious that a less costly and far more widely available source is desirable to reap the potential benefits of bright monochromatic radiation for improved detection of small anomalous features in radiography procedures such as mammography, for general medical use.
Another very effective killer is coronary artery disease, which if left undetected, and consequently untreated, has an overwhelming potential to cause premature death of the affected person. The accumulation of atherosclerotic lesions in the coronary arteries can result in complete occlusion of an artery and the onset of a heart attack. Currently, the only reliable procedure for determining the location and severity of narrowing of the coronary arteries is an x-ray angiogram in which these vessels are opacified by the direct injection of a contrast, or opacifying, agent. Differential Angiography is an important diagnostic procedure used to view the circulatory system. In this procedure, a dye (usually an iodine compound) is injected into the blood flow to make the blood flow visible. Unfortunately, this is a dangerous procedure since it requires that a catheter be employed for injection of the contrast agent. The catheter is inserted into a peripheral artery and then threaded up to the heart so that the catheter tip is at the entrance of a coronary artery. Since between 0.1% and 0.3% of patients die from this test, it cannot be used as a screening test or even as a test to be done regularly on a group of patients to study the progression of coronary artery disease. If the need for the arterial catheter could be eliminated, then x-ray imaging could be done with greatly reduced risk.
An arterial catheter is currently necessary to obtain enough image contrast. The image quality is seriously degraded with a venous injection of the contrast agent because the contrast agent is diluted by about 20:1 by the time it has gone through the lungs and both sides of the heart and starts to fill the coronary arteries. An additional problem with venous injection is that part of the contrast agent bolus may still be in the left ventricle at the optimum time for taking the arterial image. This residual contrast agent produces a background which makes it difficult to see the arteries that overlay the ventricle. There are over 1,300,000 heart attacks per year in the United States--half of which are fatal. Therefore, if a safer imaging procedure were available, it would be a significant medical advance.
Monochromatic radiation from synchrotron.RTM. radiation sources for angiography of the circulatory system is discussed in detail on pages 1674-1679, Rev. Sci. Instrum. 60(7), of the July 1989 issue of the publication published by the American Institute of Physics. Very summarily, a procedure employing synchrotron radiation has been developed in which two images are produced of the target biological object using radiation above and below the absorption edge of the dye selected. The procedure is effective for its intended purpose, however, is extremely expensive and is therefore unavailable to many in need of its attributes. Again, it is clear that a less costly and far more widely available source is desirable to achieve the potential benefits of bright monochromatic radiation for improved detection of atherosclerotic lesions in the coronary arteries, thus greatly reducing the risks inherent in the prior art.